You can try write something down! like unique points which can help you remember important details.
don't worry buddy....its often happened that we feel like we forgot everything...even that time when we got our question paper but after stated writing, everything comes in our mind automatically....only you just need to revise, write and give your best.
Read slowly and try to understand each & every line properly. If you understand the concept once.... it will be way easy to memorize. It will take time but it will help your to recall the notes..
The key is always writing it down. Take it slow, one topic at a time, and write down what you feel is important or should be remembered. Revision is also very important. Don't jump to the next chapter or topic unless you're sure you've thoroughly learnt the current one